Phospholipase D is known to transfer a phosphatidyl group of phospholipid to a hydroxy compound. Kojic acid (KA) is a hydroxy compound which has antimicrobial activity and shows inhibitory effect on tyrosinase. By using the transfer reaction from phosphatidylcholine (PC) to KA, we synthesized five 1, 2-diacylglycero-3-phosphoryl derivatives of KA, which have different acyl groups, i.e., PK 4 (dibutyloyl), PK 6 (dihexanoyl), PK 8 (dioctanoyl), PK 10 (didecanoyl) and PK 18 which was prepared from soybean PC. Membrane perturbation potency of the PKs was examined by using rat-liver mitochondria as a model biomembrane. PK 8 and PK 10 exhibited the potency, while KA, PC, PK 4 and PK 6 did not. It is known that the antimicrobial activity of some compounds is brought about by their membrane perturbation action. However, PK 8 and PK 10 did not show antimicrobial activity. The inhibitory effect on tyrosinase of the PKs was also tested. All of the PKs suppressed tyrosinase. It is considered that the inhibitory action of KA is due to its chelation with copper of the enzyme. The oxidation of unsaturated fatty acid is accelerated by some metal ions such as copper and ferrous. PK 18 has chelation potency with copper ion, and it is soluble in oil. Therefore, PK 18 was expected to be a metal inactivator in oil. As a result of oxidation test of soybean oil and methyl oleate containing copper acetate, PK 18 was shown to be an effective metal inactivator.
